1 Technical Field
The present invention relates to techniques of forming and managing a group of devices that are allowed to copy and move digital content.
2 Background Art
In recent years, movies, music, games, and the like (hereafter referred to as “content”) can easily be acquired via means such as an internet, digital broadcasting, and package media. In general, content is distributed in an encrypted form for copyright protection. The encrypted content can be decrypted and used only by an authorized device. However, excessively tight restrictions on the use of copyrighted works impair user friendliness.
In view of this, a system that allows free use of content within an “Authorized Domain” (hereafter “AD”) such as a home is disclosed (e.g. non-patent document 3).
In this system, no more than a limited number of clients are registered in a home server, and the registered clients are allowed to freely use content held in the server.
Non-patent document 1: Tatsuaki Okamoto & Hiroshi Yamamoto, Modern Cryptography, pp. 155-156, Sangyo Tosho
Non-patent document 2: American National Standards Institute, American National Standards for Financial Service, ANSX9.57: Public Key Cryptography For The Financial Industry: Certificate Management, 1997
Non-patent document 3: IIBM Response to DVIB-CPT Call for Proposals for Content Protection & Copy Management: xCP Cluster Protocol <URL: http://www.almanden.ibm.com/software/ds/ContentAssurance/papers/xCP_DVB.pdf>